Dentinal hypersensitivity is a temporary induced pain sensation produced when hypersensitive teeth are subjected to changes in temperature, pressure or chemical action. Hypersensitivity may occur whenever the dentin or cementum of a tooth is exposed by attrition or abrasion, or when the tooth's finer root surface is exposed by periodontal disease. Dentin generally contains channels, called tubules, that allow material and energy transport between the exterior of the dentin and the interior of the tooth where the nerve is located.
One approach to control dentinal hypersensitivity involves the use of “nerve agents” or “nerve desensitizing agents” in commercial dentifrices comprising strontium ions, fluoride ions, or potassium salts such as potassium bicarbonate, potassium nitrate, potassium chloride, and the like.
Another approach to control dentinal hypersensitivity is to use “tubule blocking agents” to fully or partially occlude tubules. Examples of tubule blocking agents include polystyrene beads, apatite, synthetic or mineral hectorite clay to seal dentinal tubules, polyacrylic acid and water-soluble or water-swellable polyelectrolytes or the salts thereof.
Yet a third approach to control dentinal hypersensitivity is through the mineralization of tubules in dentin thereby counteracting the hyersensitivity problem. U.S. Pat. No. 4,183,915 discloses a one-part stable aqueous solution comprising calcium ions and phosphate ions for the remineralization of dental enamel. The solution also employs an antinucleating agent to maintain the solubility of the calcium phosphate in the presence of fluoride sources. U.S. Pat. No. 4,083,955 discloses a process of remineralizing by consecutive treatment of the tooth surface with separate solutions containing calcium ions and phosphate ions. The fluoride ions may be present in the phosphate solutions. By sequentially and separately applying calcium and phosphate ions, high concentrations of the ions penetrate into the tubules whereby they precipitate as calcium phosphate salts.
U.S. Pat. No. 5,833,957 discloses an improvement with a two-part system in which calcium and phosphate are kept separate, wherein the two compounds when dispensed are mixed and immediately applied to the teeth being treated without the requirement of successive treatments. The two-part system is necessary to prevent the reaction of the calcium, phosphate and/or fluoride salts whereby an insoluble calcium phosphate or hydroxyapatite is formed during storage, leading to the unavailability of calcium ions when the dentifrice is in use. U.S. Pat. No. 5,866,102 offers yet an improved formulation with a water soluble calcium salt, a phosphate salt, and optionally a fluoride-releasing agent. To prevent the reaction of the calcium, phosphate and/or fluoride salts, it is necessary for this system to: a) employ a stabilizing desiccating agent; or b) encapsulate or coat the salts with an oleophilic or polymeric material which prevents a reaction among the active materials.
The inventors have surprisingly formulated dentifrice compositions which control dentinal hypersensitivity through the mineralization of tubules in dentin without the need for stabilizing desiccating agents or coating/encapsulating materials.